The present invention relates to an image forming apparatus of the type using a developing liquid and more particularly to a method and a device for stirring the developing liquid.
A developing liquid applicable to an image forming apparatus of the type described consists of a solvent and toner particles dispersed therein. The image forming apparatus includes a device for stirring the developing liquid stored in a reservoir. The prerequisite with the developing liquid is that the toner particles be uniformly dispersed in the solvent at all times. However, the toner particles have greater specific gravity than the solvent and consequently precipitate in the reservoir with the elapse of time. The toner particles deposited on the bottom of the reservoir render the density of the developing liquid non-uniform both in the reservoir and a developing unit to which the liquid is fed for development. An image printed on a paper or similar recording medium by such a developing liquid has irregular density and therefore poor quality. A key to high image quality is therefore to maintain the density of the developing liquid in the reservoir uniform.
It is a common practice with the above image forming apparatus to arrange a stirrer in the reservoir. The stirrer is rotatable to stir the toner particles of the developing liquid in the reservoir so as to maintain the density of the liquid constant. Specifically, a motor has its output shaft extended to a position close to the bottom of the reservoir. A blade for stirring the developing liquid is mounted on the end of the output shaft adjoining the reservoir. The blade stirs the developing liquid in the reservoir by being rotated by the motor.
The problem with the conventional blade scheme is that a single blade must be assigned to each of a plurality of reservoirs each storing a developing liquid of particular color, increasing the cost of the apparatus. In light of this, a mechanism including gears and shafts may be connected to a single motor so as to distribute the output torque of the motor to a plurality of stirrers. With this mechanism, it is possible to reduce the cost to a certain degree.
Japanese Patent Laid-Open Publication No. 6-19269, for example, teaches a simple and economical device for feeding a developing liquid. The device taught in this document, however, has some problems left unsolved, as follows. First, a single motor or drive source cannot drive all of a plurality of reservoirs alone, depending on the configuration of an image forming apparatus and the position of the individual reservoir. Second, an extra space is necessary for accommodating shafts connected to the stirrers of the reservoirs. Third, the configuration of the individual reservoir and that of the individual stirrer or blade are limited because they must prevent the developing liquid from settling in the associated reservoir. Fourth, each reservoir must be formed with a hole for passing the shaft for rotating the stirrer disposed thereon, so that the air-tightness of the reservoir is lowered. Particularly, impurities are apt to enter the reservoir via the hole while the developing liquid is apt to leak via the hole.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 5-79559, 6-95333, 6-138624, 8-114904, and 7-334004.